////
This guide is maintained in the main Quarkus repository
and pull requests should be submitted there:
https://github.com/quarkusio/quarkus/tree/master/docs/src/main/asciidoc
////
= Quarkus - MicroProfile Health

include::./attributes.adoc[]

This guide demonstrates how your Quarkus application can utilize the MicroProfile 
Health specification through the SmallRye Health extension.

MicroProfile Health allows applications to provide information about their state 
to external viewers which is typically useful in cloud environments where automated 
processes must be able to determine whether the application should be discarded 
or restarted.

== Prerequisites

To complete this guide, you need:

* less than 15 minutes
* an IDE
* JDK 1.8+ installed with `JAVA_HOME` configured appropriately
* Apache Maven 3.5.3+

== Architecture

In this guide, we build a simple REST application that exposes MicroProfile Health 
functionalities at the `/health/live` and `/health/ready` endpoints according to the 
specification.

== Solution

We recommend that you follow the instructions in the next sections and create the 
application step by step. However, you can go right to the completed example.

Clone the Git repository: `git clone {quickstarts-clone-url}`, or download an
{quickstarts-archive-url}[archive].

The solution is located in the `microprofile-health-quickstart`
{quickstarts-tree-url}/microprofile-health-quickstart[directory].

== Creating the Maven Project

First, we need a new project. Create a new project with the following command:

[source, subs=attributes+]
----
mvn io.quarkus:quarkus-maven-plugin:{quarkus-version}:create \
    -DprojectGroupId=org.acme \
    -DprojectArtifactId=microprofile-health-quickstart \
    -Dextensions="health"
cd microprofile-health-quickstart
----

This command generates a Maven project, importing the `smallrye-health` extension 
which is an implementation of the MicroProfile Health specification used in Quarkus.

== Running the health check

Importing the `smallrye-health` extension directly exposes three REST endpoints:

- `/health/live` - The application is up and running.
- `/health/ready` - The application is ready to serve requests.
- `/health` - Accumulating all health check procedures in the application.
 
To check that the `smallrye-health` extension is working as expected:

* start your Quarkus application with `./mvnw compile quarkus:dev`
* access the `http://localhost:8080/health/live` endpoint using your browser or 
`curl http://localhost:8080/health/live`

All of the health REST endpoints return a simple JSON object with two fields:

* `status` -- the overall result of all the health check procedures
* `checks` -- an array of individual checks

The general `status` of the health check is computed as a logical AND of all the 
declared health check procedures. The `checks` array is empty as we have not specified 
any health check procedure yet so let's define some.

== Creating your first health check

In this section, we create our first simple health check procedure.

Create the `org.acme.health.SimpleHealthCheck` class:

[source,java]
----
package org.acme.health;

import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;
import org.eclipse.microprofile.health.Liveness;

import javax.enterprise.context.ApplicationScoped;

@Liveness
@ApplicationScoped
public class SimpleHealthCheck implements HealthCheck {

    @Override
    public HealthCheckResponse call() {
        return HealthCheckResponse.up("Simple health check");
    }
}
----

As you can see health check procedures are defined as implementations of the 
`HealthCheck` interface which are defined as CDI beans with the one of the 
following CDI qualifiers: 

- `@Liveness` - the liveness check accessible at `/health/live`
- `@Readiness` - the readiness check accessible at `/health/ready`

`HealthCheck` is a functional interface whose single method `call` returns a 
`HealthCheckResponse` object which can be easily constructed by the fluent builder 
API shown in the example.

As we have started our Quarkus application in dev mode simply repeat the request 
to `http://localhost:8080/health/live` by refreshing your browser window or by 
using `curl http://localhost:8080/health/live`. Because we defined our health check 
to be a liveness procedure (with `@Liveness` qualifier) the new health check procedure 
is now present in the `checks` array.

Congratulations! You've created your first Quarkus health check procedure. Let's 
continue by exploring what else can be done with the MicroProfile Health specification.

== Adding a readiness health check procedure

In the previous section, we created a simple liveness health check procedure which states 
whether our application is running or not. In this section, we will create a readiness 
health check which will be able to state whether our application is able to process 
requests.

We will create another health check procedure that simulates a connection to 
an external service provider such as a database. For starters, we will always return 
the response indicating the application is ready.

Create `org.acme.health.DatabaseConnectionHealthCheck` class:

[source,java]
----
package org.acme.health;

import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;
import org.eclipse.microprofile.health.Readiness;

import javax.enterprise.context.ApplicationScoped;

@Readiness
@ApplicationScoped
public class DatabaseConnectionHealthCheck implements HealthCheck {

    @Override
    public HealthCheckResponse call() {
        return HealthCheckResponse.up("Database connection health check");
    }
}

----

If you now rerun the health check at `http://localhost:8080/health/live` the `checks` 
array will contain only the previously defined `SimpleHealthCheck` as it is the only 
check defined with the `@Liveness` qualifier. However, if you access 
`http://localhost:8080/health/ready` (in the browser or with 
`curl http://localhost:8080/health/ready`) you will see only the 
`Database connection health check` as it is the only health check defined with the 
`@Readiness` qualifier as the readiness health check procedure.

NOTE: If you access `http://localhost:8080/health` you will get back both checks.

More information about which health check procedures should be used in which situation 
is detailed in the MicroProfile Health specification. Generally, the liveness 
procedures determine whether the application should be restarted while readiness 
procedures determine whether it makes sense to contact the application with requests.

== Negative health check procedures

In this section, we extend our `Database connection health check` with the option of 
stating that our application is not ready to process requests as the underlying 
database connection cannot be established. For simplicity reasons, we only determine 
whether the database is accessible or not by a configuration property.

Update the `org.acme.health.DatabaseConnectionHealthCheck` class:

[source,java]
----
package org.acme.health;

import org.eclipse.microprofile.config.inject.ConfigProperty;
import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;
import org.eclipse.microprofile.health.HealthCheckResponseBuilder;
import org.eclipse.microprofile.health.Readiness;

import javax.enterprise.context.ApplicationScoped;

@Readiness
@ApplicationScoped
public class DatabaseConnectionHealthCheck implements HealthCheck {

    @ConfigProperty(name = "database.up", defaultValue = "false")
    private boolean databaseUp;

    @Override
    public HealthCheckResponse call() {

        HealthCheckResponseBuilder responseBuilder = HealthCheckResponse.named("Database connection health check");

        try {
            simulateDatabaseConnectionVerification();
            responseBuilder.up();
        } catch (IllegalStateException e) {
            // cannot access the database
            responseBuilder.down();
        }

        return responseBuilder.build();
    }

    private void simulateDatabaseConnectionVerification() {
        if (!databaseUp) {
            throw new IllegalStateException("Cannot contact database");
        }
    }
}
----

NOTE: Until now we used a simplified method of building a `HealthCheckResponse`
through the `HealthCheckResponse#up(String)` (there is also
`HealthCheckResponse#down(String)`) which will directly build the response object.
From now on, we utilize the full builder capabilities provided by the
`HealthCheckResponseBuilder` class.

If you now rerun the readiness health check (at `http://localhost:8080/health/ready`) 
the overall `status` should be DOWN. You can also check the liveness check at 
`http://localhost:8080/health/live` which will return the overall `status` UP because 
it isn't influenced by the readiness checks.

As we shouldn't leave this application with a readiness check in a DOWN state and 
because we are running Quarkus in dev mode you can add `database.up=true` in 
`src/main/resources/application.properties` and rerun the readiness health check again 
-- it should be up again.


== Adding user-specific data to the health check response

In previous sections, we saw how to create simple health checks with only the minimal 
attributes, namely, the health check name and its status (UP or DOWN). However, the 
MicroProfile specification also provides a way for the applications to supply 
arbitrary data in the form of key-value pairs sent to the consuming end. This can be 
done by using the `withData(key, value)` method of the health check response 
builder API.

Let's create a new health check procedure `org.acme.health.DataHealthCheck`:

[source,java]
----
package org.acme.health;

import org.eclipse.microprofile.health.Liveness;
import org.eclipse.microprofile.health.HealthCheck;
import org.eclipse.microprofile.health.HealthCheckResponse;

import javax.enterprise.context.ApplicationScoped;

@Liveness
@ApplicationScoped
public class DataHealthCheck implements HealthCheck {

    @Override
    public HealthCheckResponse call() {
        return HealthCheckResponse.named("Health check with data")
                .up()
                .withData("foo", "fooValue")
                .withData("bar", "barValue")
                .build();
    }
}
----

If you rerun the liveness health check procedure by accessing the `/health/live` 
endpoint you can see that the new health check `Health check with data` is present 
in the `checks` array. This check contains a new attribute called `data` which is a 
JSON object consisting of the properties we have defined in our health check procedure.

This functionality is specifically useful in failure scenarios where you can pass the 
error along with the health check response.


[source,java]
----
        try {
            simulateDatabaseConnectionVerification();
            responseBuilder.up();
        } catch (IllegalStateException e) {
            // cannot access the database
            responseBuilder.down()
                    .withData("error", e.getMessage()); // pass the exception message
        }
----

== Extension health checks

Some extension may provide default health checks, including the extension will automatically register its health checks.

For example, `quarkus-agroal` that is used to manage Quarkus datasource(s) automatically register a readiness health check
that will validate each datasources: link:datasource.html#datasource-health-check[Datasource Health Check].

You can disable extension health check via the property `quarkus.health.extensions.enabled` so none will be automatically registered.

== Conclusion

MicroProfile Health provides a way for your application to distribute information 
about its healthiness state to state whether or not it is able to function properly. 
Liveness checks are utilized to tell whether the application should be restarted and 
readiness checks are used to tell whether the application is able to process requests. 

All that is needed to enable the MicroProfile Health features in Quarkus is:

* adding the `smallrye-health` Quarkus extension to your project using the 
`quarkus-maven-plugin`: +
[source,bash]
----
./mvnw quarkus:add-extension -Dextensions="health"
----

* or simply adding the following Maven dependency: +
[source,xml]
----
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-smallrye-health</artifactId>
</dependency>
----

== Configuration Reference

include::{generated-dir}/config/quarkus-smallrye-health.adoc[opts=optional, leveloffset=+1]
